1-[(8S,9S,10R,13S,14S,17S)-3-cyclopentyloxy-10,13-dimethyl-2,7,8,9,11,12,14,15,16,17-decahydro-1H-cyclopenta[a]phenanthren-17-yl]ethanone

Quingestrone (INN, USAN) (brand name Enol-Luteovis; former developmental code name W-3399), also known as progesterone 3-cyclopentyl enol ether or as 3-cyclopentyloxypregna-3,5-dien-20-one, is a semisynthetic, steroidal, pure progestin that was developed by Vister and introduced in Italy as an oral contraceptive (in combination with ethinyl estradiol or mestranol) in the early 1960s. It is closely related to progesterone, being the 3-cyclopentyl enol ether of the sex hormone, and acts as a prodrug to it via slow hydrolysis in the body.
In accordance with its nature as a prodrug to progesterone, quingestrone produces identical metabolites (e.g., pregnanediol and allopregnanediols), although with differing ratios. Relative to progesterone, the drug shows improved pharmacokinetics, including higher potency, oral activity, and a longer half-life and hence duration of action due to higher lipophilicity; it is sequestered into and slowly released from fat. Quingestrone also shows slower metabolism and more stable blood levels, with a longer time to peak concentrations and a less intense peak compared to progesterone. Quingestrone is the only clinically available progestogen that converts to progesterone, and hence, is the sole progesterone prodrug to have been introduced for clinical use.
Along with the retroprogesterone derivative dydrogesterone, quingestrone is described as a "true" progesterone derivative due to its close similarity to natural progesterone. Similarly to progesterone, dydrogesterone, and hydroxyprogesterone caproate, quingestrone is a pure progestogen and lacks any androgenic effects. As such, it poses no risk of androgenic side effects or virilizing teratogenic effects on female fetuses. Accordingly, the drug was studied in the clinical prevention of miscarriage during pregnancy; however, insufficient efficacy was observed at the dosage assessed (100mg/day p.o.). Quingestrone is said to influence the hypothalamic-pituitary-adrenal axis similarly to progesterone and medroxyprogesterone acetate, producing adrenal suppression at sufficiently high doses, and this suggests that it possesses (very) weak glucocorticoid properties similarly to progesterone.
The bioavailability of quingestrone is greatest when it is given as a sesame seed oil solution (compared to an oil suspension (~2-fold less) or micronization (~7-fold less)).